Paper is typically made by feeding a uniform continuous stream of a dilute water suspension of cellulose fibers to a forming section. The forming section can include a Fourdrinier type wire machine, a twin-wire machine, or any other machine where moisture is removed from the paper pulp through wire mesh screens to produce paper stock material. The removal of moisture is typically facilitated through the use of rolls and suction boxes that support the wire screens. Upon leaving the forming section, the paper stock material typically includes about 20% solids.
The paper stock material is then transferred to the press section where it is placed onto a continuous felt. A series of press rolls are used to further remove moisture from the paper stock material through the felt by mechanical pressure. The resulting paper web is then fed to a first set of dryers to produce paper having 80-95% fiber content. The coated paper then passes through a size press where sizing agents are applied to decrease the moisture absorbency of the paper. The paper web can then be passed through two transfer rolls or through a similar device in a coating station where “coating color” is applied. Coating color typically includes fillers or pigments (e.g. calcium carbonate), binders, and the like and is typically used to impart certain properties such as whiteness, density or glossiness to the paper. The paper web is then passed to a second set of dryers and then collected, for example, on rolls.
It is often desirable to add a dye during the papermaking process to produce colored paper or patterned paper. Colored paper and patterned paper are commonly used to provide paper products having an enhanced aesthetic appearance. Colored paper is dyed evenly over its whole surface to produce a paper having a uniform color. Patterned paper is paper that has been dyed non-uniformly rather than evenly over its whole surface.
The typical method of producing dyed papers such as colored or patterned papers is to apply a dye, generally in an aqueous composition, either to the surface of the paper web during the papermaking process or to the surface of the paper after it has dried. For example, the dye can be applied by spraying the paper web with a dye composition after it has been coated and dried. Alternatively, the dye composition can be applied before the paper web has been fully dried through the use of rod, blade or roll coating methods.
Although conventional papermaking processes allow for the production of a variety of colored and patterned papers, there is a need to improve these processes. In particular, one problem with colored and patterned papers it that the colors have a tendency to bleed. As a result, the appearance of the colored or patterned paper can be adversely affected. Therefore, there is a need to produce colored or patterned papers that have good bleed resistance and thus maintain their dyed appearance.